The present invention pertains to apparatus for manipulating sheet material, and more particularly pertains to an assembly table for positioning and rotating thereupon glass sheet material so that a sealant strip material can be applied successively to all the perimeter edges of the sheet material.
A number of production steps are required in the manufacture of glass units for placement within window and door frames. Thermally insulative, single and multi-pane door and window units include a number of structural elements: wood, aluminum or vinyl frames to encase the glass window; metal spacers which are placed between the multi-pane glass window and along the peripheral edge thereof, the metal spacers sometimes being filled with a dessicant material to absorb moisture; muntin and mullion strips, commonly of wood, placed between and contiguous to each glass sheet of the multi-pane window for providing an ornamental appearance, and sealant strip material applied to the perimeter edges of each glass sheet of the multi-pane unit and in which the metal spacers are embedded.
Recent innovations in the manufacture of thermally insulative multi-pane windows include suspension of a polyester film coated with a heat insulative material between the panes of glass, and filling the space therebetween with a low conductivity gas, such as argon or krypton, which create a barrier to conductive heat transfer. The polyester film or films placed between the multi-pane window unit provides a barrier to radiative heat transfer through the window to the external environment.
It is well-known in the manufacture of single or multi-pane window units that the manner of treatment and construction of the perimeter edges is critical to the performance of the window. The manner in which the perimeter edges of the glass sheet are made can have a performance-degrading effect on the glass sheet when installed as an insulated door or window unit. The perimeter edge of the glass sheet can have a great impact on the overall thermal performance of the insulated window insofar as the center of the glass may register a high R value, yet the edges of the glass will be colder, especially during the winter, resulting in the formation of condensation between the glass sheets of the multi-pane window. This is partially due to the fact that the spacers placed at the edges of the glass sheets are predominantly made of metal which is an excellent heat conductor.
In addition, the thermal performance of the glass, whether installed as a single or multi-pane window unit, is effected by the manner in which the sealant strip material is applied to the perimeter edges thereof. Sealant strip material for application on the perimeter edges of the glass sheet comes in a number of substances, the most common being a polyisobutylene, or butyl hot melt, adhesive or a polymerizable plastic material injected by a nozzle placed adjacent the perimeter edges of the glass sheet. The sealant strip material is applied to the glass sheet to provide a hermetic barrier in the area where the frame fits around the perimeter edges of the glass sheet. Thus, moisture seepage and conductive heat loss are prevented by the airtight adhesion of the sealant strip material around the edges of the glass sheet. In a multi-pane window the sealant strip material is applied to the perimeter edges of each glass sheet to provide an air and watertight hermetic seal between the edges of both glass sheets and the window frame. The adhesive properties of the sealant strip material are designed to prevent fogging problems from developing due to a sealant strip leak, either between the sealant strip and the edge of either one or both of the glass sheets or between the sealant strip and the wood, aluminum or vinyl frame unit in which the multi-pane window is encased. When the hermetic adhesion of the sealant strip material fails, moisture in the air enters and condenses in the space between the glass panes, and fogging occurs. Thus, the quality of the multi-pane window is marred by the fogging occuring between the glass sheets, and, also, the heat insulative qualities of the multi-pane window are degraded by the sealant strip leak.
From the foregoing, it is obvious that the application of the sealant strip material is a critical element in the overall manufacture and thermal performance of any glass unit, whether a single pane or multi-pane glass window.
The prior art discloses a number of devices for applying a sealant strip material to the perimeter edges of glass sheet material. Some examples of the prior art are the Bowser et al. U.S. Pat. No. 3,886,113; the Mercier et al. U.S. Pat. No. 3,990,570; the Mercier et al. U.S. Pat. No. 4,088,522; the Mercier et al. U.S. Pat. No. 4,145,237; and the Leopold et al. U.S. Pat. No. 4,546,723.
Despite the ingenuity of the foregoing devices there is a need for an assembly table on which the application of sealant strip material to the perimeter edges of variously sized sheet material, primarily glass sheet material but not exclusively limited thereto, can be accomplished in a simple and efficient manner; avoiding systems employing extrusion nozzles, rollers upon which the sheet material longitudinally traverses, and various stations through which the glass sheet material must pass during the application process. Furthermore, there is a need for an assembly table on which sealant strip material can be applied to the edges of a glass sheet avoiding the problem of sealant strip material coating or soiling various mechanisms on the assembly table so that when the next glass sheet is placed thereupon, it is stained and soiled by sealant remnants deposited during application on the previous glass sheet.
Furthermore, there is a need for an assembly table which reduces worker movement to a minimum by successively presenting, parallel and adjacent to the workman, a perimeter edge of the glass sheet for applying sealant strip material thereto.